Waterproof fuse



"our" Patented July 4, 1950 VVATERPROOFX FUSE Henryk Zenftman, Saltcoats; Scotland, assignor to Imperial Chemical Industries Limitedyacor poration of Great Britain N0. Drawing. Application Qctober, 6, 19%, Se,-

rial No. 557,559. 1943 8 Claims. IV

The present invention relates to the manufactured non-detonating fuses for blasting and the like operations; and" more especially of safety fuse, of-the kind in which the core of self-combustible materialenclosed in the envelope comprises .a coherent rod of imporous composition formed by an extrusion of the composition ina thermoplastic condition.

Although safety fuse is usually made by enveloping a stream of a loose blackpowder composition in a suitable textile envelope, passing the resulting core through a die and applying waterproof coatings, fuses having a coherent waterproof'core made by extrusion of a thermoplastic mixture containing nitrocellulose gelatinised with nitroglyoerine and suitable pulverulent oxidising and reducing agents have atvarious timesbeensuggested in order toprevent water leaking through faults in the envelope extinguishing the fuse, but-such fuses have hitherto foundonly limited applicationon account of their undesirable sensitiveness to friction andshock.

It has also been, proposed. in British, Patent No. 544,252, (corresponding to U. S Patent No, 2,363,569,. Caldwell et. a1.) with similar objects to formalwaterproof non-detonating safety fuse of thekind having, a coherent, imperforate extruded core,- of plastic material surroundedrby an envelope of less combustible or uninfiammable material, whereof the;core comprises. aldeflagrat: ingmixture of normallypulverulent oxidising and reducing agents and a non-detonating binding agent: therefor, including gelatinised, nitrocellu-r lose but freefrom.nitroglycerine,.the weight, of the binding agent in the core compositinbei 'lg notmorethan that of the mixture: of oxidising and reducingagenta Unless i a volatile solvent for the nitrocellulose is. employed, in which case the extruded core must be exposed for a long period in order to evaporate oil the, solvent, before the outer coveringsare applied, the incorporation of'themix ture of pulverulent oxidising and reducing agents with, the binding agent containing the nitrocellulose gelatinised' with a plasticiser, and also the" extrusion of the resulting composition, must" be carried out at a high temperature in order to render the composition workable, Nitrocellulose is itself a selfr-combustible material having an unusually low spontaneous ignition temperature; and the spontaneous ignition temperature ofrthecorecompositionris substantially/lower than that of; any mixture of: pulverulent: oxidising and: reducingagents; that would; in practice be used? in it: These, manufacturing: operations are In Great Britain, October 6 therefore: attended :by a-esubstantial fire risk, and

the gelatinisatiom of the nitrocellulose with the plasticiser isalsoattendedby a certain hazard. Moreover, inthe :caseof certain-inorganic oxidisingagents thedifiiculty is frequently encountered that th'ey cause. the=binding power of the nitrocellulose' pla-stic to deteriorate more'or less rapidly at the-hightemperaturesused: I

We havenow found that serviceable orimproved fuses of 'thekind described can be produced-with greater. safety orwith greater facility from pulverulenta'oxidising and reducing agents capable :of"reactionwith sufficient f vigour, if the thermoplastic bindingagent with which they: are made into a plastic-at-zraisedtemperature is-a composition-that is based upon-a water insoluble resinous polymerisedunsaturated compound, and becomesfluent .a;t-a temperature betweenabout -and -about--C:

According to the,- present; invention a nondetonatingfuse Of? thekinds described comprises a thermoplastic binding agent comprising a water-insoluble;resi-nous polymerisedunsaturated compound" which becomes fluentat a temperature between about 90 and about/125C." anda mixturev of: pulverulent oxidising and' reducing agentscapableof reacting therein with such intensity as topermit continuous propagation of combustion;

The water-insoluble resinouspolymerised unsaturated compound may be, for, instance, -a polymerised ester or nitrile of-acrylic or methacrylic acid, a polymerised vinyl'ester of an inorganicacid; a polyvinyl acetal, or a polymerised unsaturated hydrocarbonI such- 1 as polystyrene or polymerisedethylene; A: plasticiser'-for--the-po1ye merisedr unsaturated compound may; be included in the composition.- Normal; phthalicestersi' or phosphoric estersmay be fused.

A suitable mixtureofipulverulent ox-idisinga-nd reducing agents is one, comprising silicon: and alead compound thermally decomposable-to yield products comprising. lead n onoxidesand free oxyggen; Exampleslof. such leadcompounds are the higher oxides of lead assforexample red lead'and leadperoxide,- and, lead, nitrate. Substantially gasless mixtures can. for instance be obtained from red, lead and silicon, which, des rably,- con a nia e cesslq z liconup o-a ut 25%: n, the stoichiometric mixture, If,- desired, these mix,-v turesmay. be modifiedbyithe substitution of po; tassium, nitrate or barium. nitrate for a, portion of the lead compound, as the oxidising constituent of the mixture, wherein; for, example; there may be conveniently present n9teless-thanabout tained is extruded at a suitably elevated tempera-' ture, the temperature being not higher than about 125 C. Temperatures of a range from about l00-l20 C. are usually convenient to employ in carrying out these operations, the temperature of extrusion being the higher of the two.

In general the speed of a fuse prepared from a'given mixture' of oxidising and reducing agents according to the present invention is slower than that of a fuse prepared from the same Lmixture of oxidisin and reducing agents with a, plasticised nitrocellulose binder; and the higher the proportion of binding. agentto the mixture, the lower the speed of the fuses An important safety advantage is that. the flame does not race from end to end of the core made according to the invention evenif the envelope is not closely applied. The speed of the fuse maybe somewhat increased by extruding the core composition around a soft metal wire, for instance, a copper wire'of -40 Standard wire gauge diameter. t

In making up the core composition, it is usually preferable-to work either the pulverulent oxidising agent or the pulverulent reducing agent into the thermoplastic binding agent, and subsequentlywork in the pulverulent reducing agent or oxidising agent component 'as the case may be, rather than work in'a' pulverulent mixture of the oxidising'and reducing components, or rather than work both pulverulent components in simultaneously. V

Thermoplastic binding agents based on resinous polymerised unsaturated compounds 'frequently have better binding properties than those based on nitrocellulose, so that a higher proportion of the pulverulent ingredients can be used in making up the core composition according to the present invention. The density of the pulverulent ingredients has a considerable influence'on the amount of the thermoplastic bind.- ing agent required, the denser the composition the less binding agent being required. For instance in'the case of the aforesaid mixtures of pulverulent oxidising and reducing 'a'gentscomprising red lead as an oxidising ingredient, a thermoplastic "binding agent composed of approximately equal parts of polymethyl methacrylate'and dibutyl phthalate is capable of binding from about 6.7 to 8.3 times its weight of the pulverulent mixture, whereas a thermoplastic binding agent composed of equal parts of industrial nitrocellulose and dibutyl phthalate can only bind about half ,o'f'these amounts, the oxidising and reducing agents being in each case mixed into the thermoplastic binding agent in a low pressure steam heated mixer and yielding a core composition'that can be satisfactorily extruded from a machine having an extrusion head heated to'the same temperature. In these mixtures thered lead is the most dense of the pulverulent'ingr'edients;

In fuses of the kind described made with a thermoplastic binding agent comprising a plasticised nitrocellulose composition, the binding agent takes a prominent part in the combustion of the core and is substantially burned away to form gaseous products, but in the fuses made according to the present invention the evidence provided by the products of the destructive distillation of the core composition as the fuse burns indicates that the binding agent undergoes little actual combustion.

The fact that according to the present invention a higher proportion of pulverulent oxidising and reducing agents can be included in the composition of the core and the fact that the binding agent is less eifectively consumed as the fuse burns, than in the case of fuse of the kind described made with a thermoplastic binding agent based on nitrocellulose, facilitate the production of fuses yielding a larger amount of ash and a smaller amount of gas from the core. Such fuses are subject to a smaller variation in burning speed. under varying atmospheric pressures, and when oxidising and reducing agents that react with a negligible evolution of gas are employed according to our invention, the'fus'es show very little variation indeed in burning speed with varying pressure. Furthermore, they burn more satisfactorily than prior fuses when immersed in a bulk of water.

It is a further advantage of the invention'that the binding power of the resinous polymerised unsaturated compounds is substantially unaffected by the maintenance of the core composition at the elevated temperature at which it is extruded.

The invention is illustrated in the following examples, in which the parts are parts by weight:

Example 1 20 parts of silicon sieved to pass through. a ZOOinesh British Standard specification screen are gradually worked into 12 parts of a thermoplastic binding agent composed of methyl methacrylate polymer 48 per cent and dibutyl phthalate 52 per cent contained in a. steamjacketed Werner-Pfleidere'r mixing machine, at a tem- 'perature of about C., until the silicon is well distributed through the plastic. 80 parts of the red lead powder as used in paints are worked into theplastic, the temperature being allowed to rise to about C. The action of the machine is continued until the red lead is well distributed and the mixture has a coherent plastic consistency. g

The resulting composition is transferred to an extrusion machine having a cylindrical die of 0.06 inch diameter heated to about C. When the core so extruded has cooled sufiiciently to solidify, a cotton yarn covering and countering are spun round it, and it is coated with bitumen and guttapercha and again countered with cotton yarns and finally-coated with acolour varnish made from glue, starch and china clay. The burningsspeed of the resulting waterproof safety fuse is about seconds per yard at ordinary atmospheric pressure.

Example 2 The procedure is the same as in Example 1 except that the ingredients of the core composition are used in the proportions silicon 25 parts, red lead 75 parts and binding agent 13.3 parts. The burning speed at atmospheric pressure-1s about 166 seconds per yard, and at 150. mm. pressure about 176 seconds per yard.

Example 3 The quantities and procedure are as in Example 2, except that a 36 Standard wire gauge copper wire is pulled centrally through the die at the same rate that the plastic composition is extruded around it. The burning speed of the resulting safety fuse at atmospheric pressure is about 119 seconds per yard.

Example 4 The quantities and procedure are as in Example 1, except that a 36 Standard wire gauge copper wire is pulled centrally through the die at the same rate that the plastic composition is extruded around it. The burning speed of the resulting safety fuse at atmospheric pressure is about 125 seconds per yard.

Example 5 The inorganic ingredients are silicon, red lead, and potassium nitrate, of which there are used respectively 23.8 parts, 54.4 parts and 21.8 parts. The red lead and the potassium nitrate, which is screened to pass a 100 mesh British Standard specification screen are mixed together and the mixture is introduced into a hot plastic composition containing 23.8 parts silicon distributed through 13.64 parts of a binding agent composed of methyl methacrylate polymer 48 per cent and dibutyl phthalate 52 per cent. In other respects the preparationof the waterproof safety fuse is carried out as described in Example 1. The burning speed of the resulting fuse at atmospheric pressure is about 190 seconds per yard.

Example 6 The ingredients of the core composition are the same as in Example 5, and are present in the proportions, silicon 35.25 parts, red lead 46.25 parts, potassium nitrate 18.5 parts, and binding agent 15.0 parts. The procedure is otherwise the same as in Example 5. The resulting waterproof safety fuse has a burning speed of about 144 seconds per yard at atmospheric pressure.

Example 7 The proportions of the ingredients present in the core composition are, silicon 33.6 parts, red lead 52.2 parts, potassium nitrate 14.2 parts, and binding agent 13.0 parts. The procedure is otherwise the same as in Example 5. The burning speed of the resulting waterproof safety fuse at atmospheric pressure is about 121 seconds per yard.

Example 8 The proportions of the ingredients present in the core composition are silicon 30.0 parts, red lead 50.0 parts, potassium nitrate 20.0 parts, and binding agent 14.3 parts. A 36 Standard wire gauge copper Wire is pulled centrally through the extrusion die at the same rate as the core composition is extruded around it. Otherwise the procedure is the same as in Example 5. The burning speed of the resulting waterproof safety fuse at atmospheric pressure is about 100 seconds per yard.

Example 9 The proportions of the ingredients present in the core composition are silicon 25.0 parts, red. lead 75.0 parts, and binding agent 13.0 parts.

The core composition is prepared in the manner described in Example 1 and extruded around a 36 Standard wire gauge copper wire, as described in Example 3. A jute covering and a cotton countering are then spun around the core when it has cooled sufiiciently to solidify, and subsequently the textile covered core is coated by extruding around it a layer of plastic waterproofing composition comprising polyvinyl chloride, dibutyl phthalate and tricresyl phosphate through a suitably heated die. The resulting waterproof safety fuse has a burning speed of about seconds per yard at atmospheric pressure.

Example 10 The quantities and procedure are the same in Example 6 except that a 34 instead of a 36 Standard wire gauge copper wire is used. The burning speed at atmospheric pressure is about 90 seconds per yard.

Example 11 The proportions of the pulverulent ingredient and the amount are the same as in Example 8, except the type of thermoplastic used as a binding agent which is comprised of 70% of vinyl acetate polymer and 30% dibutyl phthalate. A 33 Standard wire gauge copper wire is pulled centrally through the extrusion die at the same rate as the core composition is extruded around it. Otherwise the procedure is the same as in Example 8.

The burning speed of the resulting safety fuse at atmospheric pressure is about 150 seconds per yard.

Example 12 The proportions of the pulverulent ingredient and amounts of binding agents are the same as in Example 8 except that the thermoplastic used as a binding agent, is composed of 65% of vinyl acetate polymer and 30% dibutyl phthalate. A 33 Standard wire gauge copper wire is pulled centrally through the extrusion die at the same rate as the core composition is extruded around it. Otherwise the procedure is the same as in Example 8.

The burning speed of the resulting safety fuse at atmospheric pressure is about 140 seconds per yard.

Example 13 The inorganic ingredients are red lead, barium nitrate, and silicon, of which there are used respectively 50 parts, 50 parts and 35 parts. parts of this mixture of inorganic ingredients are homogeneously admixed with 15 parts of a binding agent composed of methyl methacrylate polymer 55% and dibutyl phthalate 45%.- In other respects the preparation of the waterproof safety fuse is carried out as described in Example 1. The burning speed of the resulting fuse at atmospheric pressure is 500 seconds per yard.

Example 14 The inorganic ingredients are lead nitrate and silicon of which there are used respectively 65 parts, and 35 parts. 90 parts of this mixture of inorganic ingredients are homogeneously admixed with 15 parts of a binding agent composed of polystyrene 65% and dibutyl phthalate 45%. In other respects the preparation of the waterproof safety fuse is carried out as described in Example 1. The burning speed of the resulting fuse at atmospheric pressure is 280 seconds per yard.

7 i I claim: s

1. A waterproof non-detonating fuse suitable for blasting and like operations, having a selfcombustible core enclosed in a protective envelope, said core being an imporous, coherent, rod-like body of a homogeneous thermoplastic composition comprising a water-inso1uble resinous polymerized unsaturated compound which becomes fluent at a temperature between 90 and 125 C. and is not readily combustible, in and throughout which are incorporated and uniformly distributed, in intimate association, nor-- mally pulverulent oxidizing and reducing agents comprising a lead compound and silicon, the latter in stoichiometric excess, wherein the oxidizing and reducing agent composition has a relatively low ignition temperature in order to permit continuous propagation of core combustion and said lead compound is thermally decomposable to yield products comprising lead monoxide and free oxygen.

2. A waterproof non-detonating fuse suitable for blasting and. like operations, having a selfcombustible core enclosed in a protective envelope, said core being an imporous, coherent, rod-like body of a homogeneous thermoplastic composition comprising a water-insoluble resinous polymerized unsaturated compound which becomes fluent at a temperature between 90 and 125 C. and is not readily combustible, in and throughout which are incorporated and uniformly distributed, in intimate association, normally pulverulent oxidizing and reducing'agents comprising a lead compound and silicon, the latter in stoichiometric excess, the ignition temperature of the oxidizing and reducing agent composition being relatively low in order to permit continuous propagation of core combustion, and thesaid lead compound comprising a higher oxide of lead.

3. A waterproof non-detonating fuse suitable for blasting and like operations, having a selfcombustible core enclosed in a protective enveloped, said core being an imporous coherent, rod-like body of a homogeneous thermoplastic composition comprising a water-insoluble resinous polymerized unsaturated compound which becomes fluent at a temperature between 90 and 125 C. and is not readily combustible, in and throughout which are incorporated and uniformly distributed, in intimate association, normally pulverulent oxidizing and reducing agents comprising red lead and silicon, the latter in stoichiometric excess, the ignition temperature of the oxidizing and reducing agent composition being relatively low in order to permit continuous propagation of core combustion.

4. A waterproof non-detonating fuse as claimed in claim 3, wherein the water-insoluble resinous polymerized unsaturated compound comprises a plasticized polymerized methyl meth- ,acrylate.

5. A waterproof non-detonating fuse suitable for blasting and like operations, having a selfcombustible core enclosed in a protective envelope, said core ibeing an imporous, coherent, rodlike body of a homogeneous thermoplastic composition comprising a water-insoluble resinous polymerized unsaturated compound which becomes fluent at a temperature between and C. and is not readily combustible, in and throughout which are incorporated and uniformly distributed, in intimate association, normally pulverulent oxidizing and reducing agents comprising lead nitrate and silicon, the latter in stoichiometric excess, the ignition temperature of the oxidizing and reducing agent composition being relatively low in order to permit continuous propagation of core combustion.

6. A waterproof non-detonating fuse as claimed in claim 1,wherein potassium nitrate is included as a further oxidizing constituent of the mixture.

7. A waterproof non-detonating fuse suitable for blasting and like operations, having a selfcombustible core enclosed in a protective envelope, said core being'an imporous, coherent, redlike body of a' homogeneous thermoplastic composition comprising a water-insoluble resinous polymerized unsaturated compound which becomes fluent at a temperature between 90 and 125 C. and is not readily combustible, in and throughout which are incorporated and uniformly distributed, in intimate association, normally pulverulent oxidizing and reducing agents comprising a lead compound and silicon, the latter'in stoichiometric excess, the ignition temperature of the oxidizing and reducing agent composition being relatively low in order to permit continuous propagation of core combustion, wherein said oxidizing agent comprises red lead and potassium nitrate, there being present not less than about 1.5 parts red lead per part potassium nitrate.

8. A waterproof non-detonating fuse as claimed in claim 1, wherein barium nitrate is included as a further oxidizing constituent of the mixture.

HENRYK ZENF'IMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,805,214 Hale 1- May 12, 1931 1,877,127 Hale Sept. 13, 1932 2,165,263 Holm July 11, 1939 2,349,048 Mackey May 16, 1944 2,363,569 Caldwell Nov. 28, 1944 2,407,131 Bruson Sept. 3, 1946 2,410,801 Audrieth Nov. 12, 1946 2,416,639 Pearsall Feb. 25, 1947 2,423,427 Payn July 1, 1947 

1. A WATERPROOF NON-DETONATING FUSE SUITABLE FOR BLASTING AND LIKE OPERATIONS, HAVING A SELFCOMBUSTIBLE CORE ENCLOSED IN A PROTECTIVE ENVELOPE, SAID CORE BEING AN IMPOROUS, COHERENT, ROD-LIKE BODY OF A HOMOGENEOUS THERMOPLASTIC COMPOSITION COMPRISING A WATER-INSOLUBLE RESINOUS POLYMERIZED UNSATURATED COMPOUND WHICH BECOMES FLUENT AT A TEMPERATURE BETWEEN 90* AND 125*C. AND IS NOT READILY COMBUSTIBLE, IN AND THROUGHOUT WHICH ARE INCORPORATED AND UNIFORMLY DISTRIBUTED, IN INTIMATE ASSOCIATION, NORMALLY PULVERULENT OXIDIZING AND REDUCING AGENTS COMPRISING A LEAD COMPOUNT AND SILICON,, THE LATTER IN STOICHIOMETRIC EXCESS, WHEREIN THE OXIDIZING AND REDUCING AGENT COMPOSITION HAS A RELATIVELY LOW IGNITION TEMPERATURE IN ORDER TO PERMIT CONTINUOUS PROPAGATION OF CORE COMBUSTION AND SAID LEAD COMPOUND IS THERMALLY DECOMPOSABLE TO YIELD PRODUCTS COMPRISING LEAD MONOXIDE AND FREE OXYGEN. 